feat: pass renderPageItem to sub navigation items

[George-Madeley]

• I've read and followed the contributing guide on how to create great pull requests.
• I've updated the relevant documentation for any new or updated feature.
• I've linked relevant GitHub issue with "Closes Customization of Navigation Menu Items #4581 ".
• I've added a visual demonstration in the form of a screenshot or video.

Summary

This PR adds support for customising the render of DashboardSidebarPageItem for child items., addressing #4581

Changes

Passed the renderPageItem function prop to DashboardSidebarSubNavigation in the renderNestedNavigation of the pageItemContextProps.

API Usage

Exactly as stated in the (docs)[https://mui.com/toolpad/core/react-dashboard-layout/#custom-page-items] but now child DashboardSidebarPageItem can now be customized. Given, the example in the documentation, to customise Sub-Item 1 and 2, a developer would do the following:

const renderPageItem = React.useCallback(
    (item: NavigationPageItem, { mini }: { mini: boolean }) => {
      ...
      if (item.title === 'Custom Item') {
        return <CustomPageItem item={item} mini={mini} />;
      }
      if  (item.segment === 'sub-item-1' {
        return <CustomPageItem item={item} mini={mini} />;
      }
      if  (item.segment === 'sub-item-2' {
        return <CustomPageItem item={item} mini={mini} />;
      }
      return <DashboardSidebarPageItem item={item} />;
    },
    [],
  );

It might be better to have the full path rather than the segment.

Documentation

No documentation required as the current documentation implies that this is already possible.

Close #4581

[mui-bot]

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